reading from the title I though the sun are more rounder at oversea, so need some special filter.... ;p
anyway, we can't recommend just ONE type of filter as each day sunrise may NOT be the same.
I have Cokin GND, hi-tech GND soft 0.3, 0.6 and 0.9, ND4, ND400, CPL and ND fader, and I still it won't suit all the situation I encounter.